The invention relates to processes and machines for the local treatment of drinking water by means of ion exchange, adsorption at surfaces and UV irradiation. The basic processes for the treatment of drinking water by means of ion exchange, for example the softening or decarbonization of drinking water, the removal of nitrate ions by means of nitrate-selective exchanger resins or the adsorption of organic impurities on active carbons or molecular sieves, are sufficiently known and are used in numerous processes and appliances. Appliances employing these processes are offered by various companies for the treatment of drinking water in the domestic sector. For example, the water filter jugs of the BRITA company for the softening of water (referred to below as table-top appliances) or the water filter systems of the BIOLIT company for the removal of nitrate and designed for direct connection to the water pipeline (referred to below as tapping-point appliances) are known. Essential components of these appliances are filter cartridges filled with ion exchangers and active carbon. The filter cartridges have only a limited capacity and therefore have to be replaced or regenerated regularly.
The known processes and appliances have, however, several basic weak points which are decisively improved by the processes described here and their embodiments. Problems in the case of the known appliances are, on the one hand, the risk of bacterial contamination of the drinking water and, on the other hand, the fact that the monitoring of the exhaustion of the used filter cartridge has been solved only to an inadequate extent. Furthermore, in the case of these appliances, the theoretically possible filter capacity of the filter materials used is only utilized to an insufficient extent because of the simple control of the process. In addition, the water quality of the treated water varies very considerably with the operating time of the filter materials used in the appliances. Furthermore, the known table-top appliances need separate feedstock tanks for the untreated and treated water.